CONCRETE DESIGN 295 



should be placed over each support at the top of the beam 

 to withstand this moment. This steel should extend far 

 enough on each side of the support to reach the point where 

 the bending moment changes sign. In many cases one- 

 quarter of the span each way will be sufficient. This steel 

 is often made up partly of rods bent up from the bottom of 

 the beam and partly from extra rods inserted at the top. 

 For both beams and slabs for interior spans of continuous 

 beams the Joint Committee recommends that the bending 



Wl 

 moment be taken as , both at the center of the span and 



over the support. In beams for end spans and the adjoining 



Wl 

 support, the bending moment should be taken at . After 



the bending moment is found, the beam is designed in the 

 manner already stated. 



Some engineers claim this reduction in bending moment 



Wl 



is unwarranted and use for all cases. No matter which 

 8 



method is followed, the beam should be reinforced over the 

 support. 



Caution must be exercised in designing continuous 

 T beams. At the support, the compression in the concrete 

 is apt to be excessive, as it comes on the stem of the T. 

 The Joint Committee allows a higher stress in the concrete 

 here and recommends a value approaching 750 Ib. It is 

 often necessary to leave some steel at the bottom oi 

 T beams near the supports to assist in withstanding this 

 compression. 



Beams Reinforced at Top and Bottom. For beams rein- 

 forced at the top and bottom, the preceding notation, with 

 the following additional characters, is employed: 



A' area of compressive steel at top of beam, in square 

 inches; 



A> 



p' = ratio of area of compressive steel to bd = ; 



bd 



Ff= compressive stress in steel, in pounds per square inch; 

 rf' = distance from top of beam to top steel, in inches. 



